1. Field of the Invention
The invention relates to an apparatus for granulating extruded material including an extruder, an underwater granulator connected to the extruder and having a cutting plate, a feed pipe connected to the granulator for providing process water, and a discharge pipe connected to the extruder for transporting and cooling granulate.
2. Description of the Related Art
In an underwater granulator, the large number of strands of melt which have been pressed from an extruder and through a breaker plate with nozzle holes arrive at a cutting plate, where a rotating knife cuts the strands of cooled and solidified melt into small pieces, which form a granulate. Adjacent to the cutting plate is a chamber filled with process water, which serves to solidify the melt further and to transport the granulate. The granulate-water mixture is transported through a discharge pipeline to a separation device. In this device, the solidified granulate is separated from the process water, and it is then dried. The underwater granulator is connected to the extruder during operation, usually by means of a flange. So that maintenance work such as the replacement of the cutting plate can be performed, the granulator must be detached from the extruder. So that the assembly and disassembly work can be carried out quickly, it has been found advantageous for the underwater granulator to be attached to the extruder by a movable joint, so that the granulator can be detached from the extruder simply by swinging it away. It can then be reattached to the extruder by swinging it back into position.
In a swinging granulator of this type, however, the problem remains that the process water feed and discharge lines must be detached before the underwater granulator can be swung away, and before operations can commence again after completion of the maintenance work, these lines must be reattached after the granulator has been swung back into position. To avoid this assembly/disassembly work, it would be possible to design the process water feed and discharge lines as flexible hoses. A flexible line could also be equipped with expansion joints. A hose connection, however, represents a safety problem, because the water used in the granulation process can reach temperatures as high as 90° C., and hot water escaping from a leaky or burst hose represents a potential danger. In addition, the large bending radii which hoses require sharply limits the freedom with which the unit can be designed. Systems built with connections of this type for the process water are therefore often bulky and can become too large in comparison with the size of the overall granulation system. When the underwater granulator is swing into and out of position, furthermore, the connecting hoses are subjected to torsional forces, because the connecting points at the underwater granulator rotate when the granulator is swung back and forth. The torsional stresses caused by the rotational movements of the swinging granulator, however, are damaging to the hoses over the long term. Hoses are not designed to endure continuous rotational movements around their own axes. In the case of the swinging granulators according to the state of the art, therefore, the connections between the granulator and the pipeline system are usually detached before the granulator is swung away.